Ginseng (Panax ginseng C. A. Meyer) is one of the herbs that have been traditionally used in Asian countries including Korea, China and Japan for treatment and prevention of a variety of diseases. Ginseng saponins also called ginsenosides are main active ingredients of ginseng and are known to have various physiological activities including anti-aging activity, anti-inflammatory activity, antioxidative activity in the central nervous system, cardiovascular system and immune system, anti-diabetic activity and antitumor activity.
Until now, more than 40 kinds of ginsenosides have been isolated and identified. The ginsenosides which are glycosides having a dammarane structure including aglycones may be largely classified into protopanaxadiols and protopanaxatriols. The ginsenosides belonging to the protopanaxadiol group are mainly Rb1, Rb2, Rc and Rd, and the ginsenosides belonging to the protopanaxatriol group are mainly Re and Rg1 (see FIG. 1 and FIG. 2).
After taken in, the ginsenosides are metabolized by intestinal microorganisms and the metabolic products are known to have various physiological activities. For example, the representative protopanaxadiol-based saponins Rb1, Rb2 and Rc are metabolized by human intestinal microorganisms to CK and the protopanaxatriol-based saponins Re and Rg1 are metabolized by intestinal microorganisms to Rh1 or F1, thereby exhibiting a variety of physiological activities. CK is known to induce anti-metastatic or anticancer effect of preventing invasion and formation of tumors. And, it is reported that its aglycone PPD(S) has higher physiological activity as compared to the sugar-attached counterpart Rh2.
Accordingly, studies have been made to transform ginsenosides into metabolites having less sugar. In addition to enzymatic methods, hydrolysis using weak acids, degradation using alkalis, or the like have been reported. However, since these methods induce several side reactions such as epimerization, hydration, hydroxylation, etc., methods of transforming into active ginsenosides using enzymes, intestinal microorganisms, and so forth are studied recently. But, most of the reported microorganisms are anaerobic intestinal microorganisms, there is a limit in industrial application. Also, since most enzymes lack the activity of transforming ginsenosides into aglycones and have their own specificity, they are applicable to production of specific ginsenosides only.
Although a lot of studies have been made thus far about the biotransformation of the metabolite of the ginsenoside Rb1 by intestinal microorganisms to CK, there are few researches about production of its aglycone. And, it is reported that the ginsenoside having one sugar on the saponin backbone is not degraded by the enzymes of microorganisms any more. Ginsenosides in aglycone form are known to be absorbed more easily into the bloodstream and act as active compounds. Also, the production of aglycones as backbones of various ginsenosides will make a base technology for specific production of desired types of ginsenoside. Accordingly, there is a need of exploring enzymes involved in the production of ginsenoside aglycones.